Ducted fan air vehicles may include at least one ducted fan and an engine to drive the fan inside the air duct of the ducted fan. A ducted fan air vehicle may have the ability of forward flight and stationary hovering. For example, ducted fans are known to be used with vertical take-off and landing (“VTOL”) air vehicles. However, while ducted fans may enable both horizontal and vertical flight, a traditional design requires compromise in the design features for each flight mode (e.g., horizontal and vertical flight) in order to meet overall aerodynamic performance requirements in a balanced manner. The many constraints preclude a design that maximizes aerodynamic efficiency in each operational flight mode. Thus, the aerodynamic efficiency of both flight modes suffers.
Accordingly, those skilled in the art continue with research and development efforts in the field of ducted fan propulsion.